Authorities investigated a suspicious envelope at a downtown building in the area of 3rd Avenue and Washington Street on Tuesday.

Fire officials said they received a report sometime after 8 a.m. of an envelope containing an unknown white powder substance and began working with police to evacuate the area, according to a statement from Phoenix Fire Department.

The 305 building, attached to a parking garage, houses City of Phoenix water and customer service personnel.

A man, who was not identified, was the only person exposed to the substance, according to fire officials.

"Our crews immediately began evaluating him while simultaneously working with Phoenix police to evacuate the area and isolate the area so that we would minimize who was exposed," said Capt. Jake Van Hook with the Phoenix Fire Department.

Phoenix Fire Department Hazardous Materials technicians went into the building to try to identify the substance, according to the statement.

Fire crews evaluated the man who was exposed to the substance for more than an hour, and he was found to be in stable condition, the statement said.

Police and fire crews have closed off an downtown area near 3rd Avenue and Washington Street to investigate a reported suspicious package Tuesday morning.(Photo: Nathan Fish)

After an evaluation by the fire department, the man refused transport to the hospital.

Personnel on-scene were unable to determine the type or name of the substance, according to the statement. Hazardous materials teams collected a sample of the suspicious material and will send it to the Arizona state laboratory for further evaluation.

While the attached parking garage remained open near 4th Avenue, Jefferson Street, was not reopened until just past 10 a.m.